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HTML footnotes with m4

When I worked with LaTeX I used a lot of footnotes. I don't know why but I love them!

Manually taking care of the numbering can be tedious and I felt like I should learn a little bit more m4. So I added two macros#0 to my Static Site Generator that I use to build my blog.

Let's have a look:


$ nl stddef.m4 | grep __fn
15	define(`__fnc', 0)
16	define(`FN', `$1<a href=`#'__fnc>`#'__fnc</a>define(`__fnc', incr(__fnc))')
17	define(`__fnlc', 0)
18	define(`FNL', `<li id=__fnlc>__fnlc: $1</li>define(`__fnlc', incr(__fnlc))')
In a nutshell: We have two counter variables __fnc and __fnlc and two macros FN and FNL. FN is used to mark the word the footnote is attached to and FNL to create a list entry at bottom of the page.

<p>Some text inside a HTML document that needs a footnote`'FN.</p>
...
<ul>
FNL(Nothing to see here)
</ul>
I don't want a space between the word and the footnote marker. m4 would not recognize the macro if I would write footnoteFN. One way to circumvent this is to use an empty quoted string like you see above. As I did design the macro to take a parameter you could also use FN(footnote).

The trick is that the macro we call contains a redefinition of the counter variable in which we increase the counter variable every time we invoke the macro. That way I only#1 need to keep the actual foot note entries in the correct order.